Flandymonium you don't seem to understand OP's problem, which is also my problem, this bug only happens if you hit the Army button on a selected enemy unit. It will bring you into a screen to switch their forces, but you can't exit out of it, it essentially freezes the game.

This thread actually points out two bugs, and I have also encountered the second bug the OP mentions as well. Enemy units hiding under wandering monster units. Instead of fighting they coexist. I have yet to see an enemy/non-player stack attack another non-player stack. I know they attack cities since I get the message ingame that a city was conquered by blahblahblah, but I don't see any pitched battles in the field.